Preheat the oven to 190°c/Gas 5. Line 2 12 hole cake tins with paper cases. Tip: If you don't have cake cases you can grease 2 baking trays, they will just spread a little thinner, but will still taste delicious.
Beat the butter and sugar in a bowl until soft.
Add the vanilla and egg. Sift in the cornflour and both flours and stir until combined and chill for 30mins.
Roll heaped teaspoon of the mixture into balls and the middle of each paper case. Make a deep indent into the centre of each ball with a wooden spoon handle dipped in flour.
Fill each indent with a ¼ tsp of jam Tip I fill a ¼ tsp of jam, then use the end of a teaspoon to slide the jam in the hole). Bake for about 20mins until pale golden.
Cool for a few mins, remove from the cake cases and place on a wire rack to cool completely.
Dust with icing sugar before serving.